The present invention relates to a locking device, preferably for releasable attaching a plastic wafer to articles providing security against the theft thereof and which device comprises a locking mechanism mounted in a house and intended to be attached to the wafer, and a pin member, preferably with a smooth surface, interacting with the locking mechanism.
Several types of locking devices are known which are intended for a temporarily but secure fixing of plastic wafers containing electronic detection circuits to the article which is to be secured against theft.
The locking mechanism of the locking device is contained in a house which is arranged in the plastic wafer, and this assembly is placed at one side of the article to be protected, after which a so-called pin is passed through the article and into the locking mechanism. The enlarged head of the pin placed at one side of the article together with the plastic wafer/locking mechanism assembly placed at the other side of the article hereby will prevent that the article is brougth out of a store or another especially protected area herein, as the electronic circuit in the plastic wafer by passing particular monitoring antennas will actuate an alarm system. In case the article has been purchased authorized personnel having a particular release device will release the connection between the pin and the locking mechanism and remove the pin so that the wafer may be removed from the article.
In such known locking devices the shaft of the pin is provided with circumferentially extending grooves at spaced positions. These grooves are intended for interlocking of the pin and the locking mechanism, and they are to be made with a very high accuracy of machining to obtain a secure interlocking. Moreover, the presence of the grooves in the shaft may give rise to destruction of a textile web as the shaft passes therethrough either by rupture of threads or by pulling out threads. This occurs especially in case with finely woven articles.
To prevent these drawbacks more locking devices are made wherein the cooperating pin member is provided with a smooth surface. However, these locking devices may be released by a mechanic action possibly by means of a specially provided tool and, accordingly, they are not well suited for securing goods against theft as it is relatively easy to make a non-authorized release of the locking mechanism.
Other locking devices with a smooth shaft are provided with spring biased balls or rollers which wedge the pin either by wedging between more balls or between a roller and a wall of the house. These locking devices may be released by magnetism in that the balls, a holder for the balls or the roller are made of a magnetic material.
However, these locking devices are complex and costly to make for having a satisfactory operation and a sufficient resistance against removal of the pin. Accordingly, a very high accuracy is required for machining of constituents.